Bovcon, N. D. | Search bioRxiv

bioRxiv2023

One marine protected area is not enough: The trophic ecology of the broadnose sevengill shark (Notorynchus cepedianus) in the Southwest Atlantic

O_LIThe broadnose sevengill shark (Notorynchus cepedianus) has been categorized as Vulnerable by the IUCN and shows a declining population trend in the Southwest Atlantic. Bycatch and poaching are the major threats in the region. C_LIO_LIAlthough some ecological requirements have been described, there are still several information gaps regarding its ecology. Important aspects of its trophic ecology, like main prey items or key feeding grounds, remain uncertain and are essential to design effective conservation strategies. C_LIO_LIWe applied stable isotope and stomach content analyses to describe the trophic ecology of sevengill shark within a marine protected area of Peninsula Valdes in Patagonia, Argentina. C_LIO_LIThe stomach content analysis determined the southern elephant seal, Mirounga leonina, as the most frequently regurgitated prey item (70%F) during abundance peaks of both species in Peninsula Valdes. The stable isotope analysis indicated that the overall contribution of the elephant seal to the diet of the sevengill shark was around 30% and that this percentage varied with the size of individuals. C_LIO_LIPresent results strengthen the current understanding of the trophic ecology of the sevengill shark. This study confirmed the use of the marine protected area as an essential foraging ground and identified its main prey items. Also, it reinforced the critical need to expand conservation tools beyond this particular coastal protection. C_LI

ecology↗

bioRxiv2021

Fish functional diversity as an indicator of resilience to industrial fishing in Patagonia Argentina

The relationship between fish functional diversity and fishing levels at which its baselines shift is important to identify the consequences of fishing in ecosystem functioning. For the first time, we implemented a trait-based approach in the Argentine Patagonian sea to identify the vulnerability and spatiotemporal changes in functional diversity of fish assemblages bycatch by a trawling fleet targeting the Argentine red shrimp Pleoticus muelleri (Spence Bate, 1888) between 2003 and 2014. We coupled seven fish trophic traits to a reconstructed fish assemblage for the study area and bycatch and evaluated changes in fish species richness and four complementary functional diversity metrics [functional richness, redundancy, dispersion, and community trait values] along with fishing intensity, temporal use, latitudinal location, and depth of fishing grounds. Resident fishes larger than 30 cm in TL, with depressed and fusiform bodies, intermediate to high trophic levels, and feeding in shallow benthic, benthodemersal, and benthopelagic areas were vulnerable to bycatch. Fish assemblages exhibited a low functional trait redundancy, likely related to species influxes in a biogeographic ecotone with tropicalisation signs. Significantly increases in fish trait richness and dispersion polewards and with depth suggested new functional roles in these grounds, matching trends in community body size, reproductive load, maximum depth, trophic level, and diet breadth. Finally, a temporal increase in fish species and functional trait removal in fishing grounds led to trait homogenisation since the first year of trawling. The identified tipping points in temperate fish functional trait diversity highlight trait-based approaches within ecosystem-based fisheries management.

ecology↗